U.S. patent application number 10/491726 was filed with the patent office on 2004-12-09 for high brightness wide gamut display.
Invention is credited to Roth, Shmuel.
Application Number | 20040246389 10/491726 |
Document ID | / |
Family ID | 30771116 |
Filed Date | 2004-12-09 |
United States Patent
Application |
20040246389 |
Kind Code |
A1 |
Roth, Shmuel |
December 9, 2004 |
High brightness wide gamut display
Abstract
A device to produce a color image, the device including a color
filtering arrangement to produce a plurality of primary colors,
each primary color having a spectral range, wherein the spectral
ranges of at least two of the primary colors overlap
significantly.
Inventors: |
Roth, Shmuel; (Petach Tikva,
IL) |
Correspondence
Address: |
EITAN, PEARL, LATZER & COHEN ZEDEK LLP
10 ROCKEFELLER PLAZA, SUITE 1001
NEW YORK
NY
10020
US
|
Family ID: |
30771116 |
Appl. No.: |
10/491726 |
Filed: |
April 5, 2004 |
PCT Filed: |
July 24, 2003 |
PCT NO: |
PCT/IL03/00610 |
Current U.S.
Class: |
349/5 |
Current CPC
Class: |
H04N 9/3105
20130101 |
Class at
Publication: |
349/005 |
International
Class: |
G02F 001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 24, 2002 |
US |
60397781 |
Claims
1. A device to produce a color image, the device comprising a color
filtering arrangement to sequentially produce at least four primary
colors, each primary color having a spectral range, wherein the
spectral ranges of at least two of said primary colors overlap
significantly.
2. The device of claim 1 wherein said color filtering arrangement
comprises a plurality of filter segments on a color switching
mechanism.
3. (Canceled).
4. The device of claim 1 wherein said at least four primary colors
comprise a blue color having a wavelength spectral range from about
400 nm to between 460 nm and 540 nm, a green color having a
spectral range from between 480 nm and 520 nm to between 540 nm and
580 nm, a yellow color having a spectral range from between 500 nm
and 550 nm to 650 nm or more, and a red color having a spectral
range from between 580 nm and 620 nm to 700 nm or more.
5. The device of claim 1 wherein said at least four primary colors
comprise at least five primary colors.
6. The device of claim 5 wherein said at least five primary colors
comprise a blue color having a wavelength spectral range from about
400 nm to between 460 nm and 540 nm, a cyan color having a spectral
range from between 400 nm and 460 nm to between 500 nm and 560 nm,
a green color having a spectral range from between 480 nm and 520
nm to between 540 nm and 580 nm, a yellow color having a spectral
range from between 500 nm and 550 nm to 650 nm or more, and a red
color having a spectral range from between 580 nm and 620 nm to 700
nm or more.
7. The device of claim 5 wherein said at least five primary colors
comprise at least six primary colors.
8. The device of claim 7 wherein said at least six primary colors
have spectral ranges of approximately 400-500 nm, approximately
500-550 nm, approximately 575-750 nm, approximately 450-520 nm,
approximately 520-620 nm, and approximately 620-750 nm,
respectively.
9. A device adapted to produce a color image using at least four
primary colors, the device comprising: a reflection-transmission
element to reflect an s-polarized component of received light and
to transmit a p-polarized component of the received light; a color
filtering arrangement to separate said s-polarized and p-polarized
components into at least four light beams corresponding to said at
least four primary colors; and at least four reflective LCD panels
to modulate the polarization of said at least four light beams,
respectively, to produce at least four modulated light beams
corresponding to said color image, wherein said color filtering
arrangement comprises at least one color separation cube able to
separate at least one of said s-polarized and p-polarized
components into three or more of said at least four light
beams.
10. The device of claim 9 wherein each of said primary colors has a
spectral range, and wherein the spectral ranges of at least two of
said primary colors overlap significantly.
11. The device of claim 9 comprising a projection lens, wherein
said reflection-transmission element further reflects s-polarized
components of said modulated light beams and transmits p-polarized
components of said modulated light beams onto said projection
lens.
12. The device of claim 9 wherein said deflection-transmission
element comprises a polarizing beam splitter.
13. (canceled).
14. A method of producing a color image, the method comprising
sequentially producing at least four primary colors corresponding
to said color image, each primary color having a spectral range,
wherein the spectral ranges of at least two of said primary colors
overlap significantly.
15. The method of claim 14 wherein sequentially producing said
primary colors comprises sequentially filtering light of an
illumination unit.
16. The method of claim 14 wherein said at least four primary
colors comprise a blue color having a wavelength spectral range
from about 400 nm to between 460 nm and 540 nm, a green color
having a spectral range from between 480 nm and 520 nm to between
540 mn and 580 nm, a yellow color having a spectral range from
between 500 nm and 550 nm to 650 nm or more, and a red color having
a spectral range from between 580 nm and 620 nm to 700 nm or
more.
17. The method of claim 14 wherein said at least four primary
colors comprise at least five primary colors.
18. The method of claim 17 wherein said at least five primary
colors comprise a blue color having a wavelength spectral range
from about 400 nm to between 460 nm and 540 nm, a cyan color having
a spectral range from between 400 nm and 460 nm to between 500 nm
and 560 nm, a green color having a spectral range from between 480
nm and 520 nm to between 540 nm and 580 nm, a yellow color having a
spectral range from between 500 nm and 550 nm to 650 nm or more,
and a red color having a spectral range from between 580 nm and 620
nm to 700 nm or more.
19. The method of claim 17 wherein said at least five primary
colors comprise at least six primary colors.
20. The method of claim 19 wherein said at least six primary colors
have spectral ranges of approximately 400-500 nm, approximately
500-550 nm, approximately 575-750 nm, approximately 450-520 nm,
approximately 520-620 nm, and approximately 620-750 nm,
respectively.
21. The device of claim 10 wherein said at least four primary
colors comprise a blue color having a wavelength spectral range
from about 400 nm to between 460 nm and 540 nm, a green color
having a spectral range from between 480 nm and 520 nm to between
540 nm and 580 nm, a yellow color having a spectral range from
between 500 nm and 550 nm to 650 nm or more, and a red color having
a spectral range from between 580 nm and 620 nm to 700 nm or
more.
22. The device of claim 10 wherein said at least four primary
colors comprise at least five primary colors.
23. The device of claim 22 wherein said at least five primary
colors comprise a blue color having a wavelength spectral range
from about 400 nm to between 460 nm and 540 nm, a cyan color having
a spectral range from between 400 nm and 460 nm to between 500 nm
and 560 nm, a green color having a spectral range from between 480
nm and 520 nm to between 540 nm and 580 nm, a yellow color having a
spectral range from between 500 mn and 550 nm to 650 nm or more,
and a red color having a spectral range from between 580 nm and 620
nm to 700 nm or more.
24. The device of claim 22, wherein said at least five primary
colors comprise at least six primary colors.
25. The device of claim 24, wherein said at least six primary
colors have spectral ranges of approximately 400-500 nm,
approximately 500-550 nm, approximately 575-750 nm, approximately
450-520 nm, approximately 520-620 nm, and approximately 620-750 nm,
respectively.
26. The device of claim 24, wherein said at least one color
separation cube comprises a first color separation cube able to
separate said s-polarized component into three light beams, and a
second color separation cube able to separate the p-polarized
component into three light beams.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to color display devices and
methods of displaying color images and, more particularly, to high
brightness and/or wide color gamut displays.
BACKGROUND
[0002] Various types of color display technologies are known in the
art. For example, there are CRT display systems, LCD systems, and
projection display systems. In front projection displays, the
projected images are viewed from a reflective viewing screen. In
rear projection displays, the projected images are viewed through a
transmissive viewing screen.
[0003] To produce color images, existing display devices use three
primary colors, typically, red green and blue, collectively
referred to as RGB. In sequential projection display systems, the
three primary color components of an image are modulated and
displayed sequentially, typically using a single Spatial Light
Modulator (SLM) panel. In simultaneous projection display systems,
the three primary color components of the image are modulated and
displayed simultaneously using one or more SLIM panels.
[0004] An important consideration in designing projection display
devices is the display brightness. Thus, efforts are continually
made to increase the optical efficiency of existing designs and,
thereby, to increase the luminous output that can be obtained from
a given light source.
[0005] Unfortunately, the light sources commonly used in existing
display devices, for example, the UHP.TM. lamps available from
Philips Lighting, a division of Royal Philips Electronics,
Eindhoven, Netherlands, produce non-uniform light spectra wherein,
typically, the intensity of the red wavelength range is
significantly lower then the intensity of other spectral ranges.
Thus, in existing RGB systems, typically, higher brightness may be
achieved only by significantly reducing the color saturation of the
red wavelength ranges. Further, in projection display systems for
home theater applications, wherein highly saturated colors are
typically required, filters with narrower spectral transmission
ranges are typically used, causing an additional reduction in image
brightness.
[0006] The quality of color image reproduction can be significantly
improved by expanding the color gamut of the display system. This
can be achieved by using more than three primary colors to
reproduce the image. Display systems using more than three primary
colors are described in International Applicaton PCT/IL01/00527,
entitled "Device, System and Method For Electronic True Color
Display", filed Jun. 7, 2001, and publised Dec. 13, 2001 as WO
01/95544, assigned to the assignee of the present application, the
entire disclosure of which is incorporated herein by reference.
[0007] A six-primary display using superimposed images produced by
two projection display devices, wherein each projection display
device uses three different primary colors, is described in
Masahiro Yamaguchi, Taishi Teraji, Kenro Ohsawa, Toshio Uchiyama,
Hideto Motomura Yuri Murakami, and Nagaaki Ohyama, "Color image
reproduction based on the multispectral and multiprimary imaging:
Experimental evaluation", Device Independent Color, Color Hardcopy
and Applications VII, Proc. SPIE, Vol. 4663, pp. 15-26 (2002). In
the dual-projection display system described in this reference, the
wavelength ranges selected for the six primary color filters are
essentially uniformly distributed across the visible spectra of
400-700 nm, with no spectral overlap between the primaries. In this
way, a wide gamut may be achieved; however, the combined brightness
of the two projection devices is dramatically reduced. In fact, the
combined brightness produced by this dual-projection device is
lower than the brightness produced by a corresponding single RGB
projection device. Dividing the visible spectrum into six (rather
than three) ranges does not increase the over-all image brightness
because the six primaries cover narrower sub-ranges of the same
visible spectrum. An additional reduction of intensity is caused by
inherent optical losses in the division of the spectrum into
narrower ranges.
SUMMARY OF EMBODIMENTS OF THE INVENTION
[0008] An embodiment of the present invention provides a
multi-primary color display device, e.g., a color projection
display device, which produces images having a wide color gamut at
brightness levels significantly higher than those of prior art
devices. Further, for a given light source, the brightness level
produced by embodiments of the device of the present invention is
at least equal, and in some cases higher, than the brightness level
of a conventional RGB projection display device using the same
light source.
[0009] Embodiments of the present invention increase the efficiency
of display devices by utilizing a relatively large portion of the
polychromatic light generated by a light source, compared to
conventional devices, while maintaining a relatively wide color
gamut of the displayed images. According to embodiments of the
invention, n primaries, wherein n is grater than three, may be
selected and used to utilize some or all of the conventionally
unused part of the white light generated by the light source, in
order to provide increased brightness and/or a wider color
gamut.
[0010] According to some of these embodiments, an increase in
illumination efficiency may be achieved by using partially
overlapping primary color spectra, wherein at least two of the
primary color spectra overlap significantly. A specifically
designed color filtering arrangement, e.g. including sets of
filters or other filtering elements, may be used to convert white
light into the desired, significantly overlapping spectra. The
significantly overlapping primary color spectra may allow a larger
percentage of the white light generated by the light source to be
used by the display device. For example, when the device of the
invention is operated in "full illumination" mode, i.e., when all
the primary colors are at their maximum levels, the wide color
gamut device of the invention may produce a white light output at
levels comparable to, or even higher than, those of produced by a
corresponding RGB projection device having a much narrower color
gamut.
[0011] Further, specific designs of the filterng elements and
overlap ranges of the wide gamut display of the invention may
compensate for non-uniformities and other deficiencies of the light
spectra generated by the white light source. In embodiments of the
inventon, We transmission curves of the filtering elements may be
designed specifically to maximize the display brightness for a
given gamut, whereby substantially all colors within the desired
color gamut may be reproduced at optimal efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention will be understood and appreciated more fully
from the following detailed description of embodiments of the
invention, taken in conjunction with the accompanying drawings of
which:
[0013] FIG. 1A is a schematic illustration of the spectral output
of a high-pressure mercury lamp in accordance with exemplary
embodiments of the invention;
[0014] FIG. 1B is a schematic illustration of the spectral output
of a Xenon light source in accordance with further exemplary
embodiments of the invention;
[0015] FIG. 2 is a schematic illustration of an optical
configuration for a device, in accordance with exemplary
embodiments of the invention;
[0016] FIGS. 3A and 3B are schematic illustrations of primary color
wavelength spectra for a six-primary color display using the
configuration of FIG. 2, in accordance with exemplary embodiments
of the invention;
[0017] FIG. 4 is a schematic illustration of the color gamut
resulting from the primary color spectra of FIGS. 3A and 3B;
[0018] FIG. 5 is a schematic illustration of primary color
wavelength spectra for a five-primary color display in accordance
with one exemplary embodiment of the invention;
[0019] FIG. 6 is a schematic illustration of the color gamut
resulting from the primary color spectra of FIG. 5;
[0020] FIG. 7 is a schematic illustration of primary color
wavelength spectra for a five-primary color display in accordance
with another exemplary embodiment of the invention; FIG. 8 is a
schematic illustration of the color gamut resulting from the
primary color spectra of FIG. 7;
[0021] FIG. 9 is a schematic illustration of primary color
wavelength spectra for a four-primary color display in accordance
with one exemplary embodiment of the invention;
[0022] FIG. 10 is a schematic illustration of the color gamut
resulting from the primary color spectra of FIG. 9;
[0023] FIG. 11 is a schematic illustration of primary color
wavelength spectra for a four-primary color display in accordance
with another exemplary embodiment of the invention; and
[0024] FIG. 12 is a schematic illustration of the color gamut
resulting from the primary color spectra of FIG. 11.
[0025] It will be appreciated that for simplicity and clarity of
illustration, elements shown in the figures have not necessarily
been drawn accurately or to scale. For example, the dimensions of
some of the elements may be exaggerated relative to other elements
for clarity or several physical components included in one element
Further, where considered appropriate, reference numerals may be
repeated among the figures to indicate corresponding or analogous
elements. It will be appreciated that these figures present
examples of embodiments of the present invention and are not
intended to limit the scope of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0026] In the following description, various aspects of the present
invention will be described. For purposes of explanation, specific
configurations and details are set forth in order to provide a
thorough understanding of the present invention. However, it will
be apparent to one skilled in the art that the present invention
may be practiced with out the specific details presented herein.
Furthermore, some features of the invention relying on principles
and implementations known in the art may be omitted or simplified
to avoid obscuring the present invention.
[0027] The following description of exemplary embodiments of the
invention is based on a projection display system using a
high-pressure mercury lamp, e.g., the UBP.TM. 100 Watt lamp,
available from Philips Lighting, a division of Royal Philips
Electronics, Eindhoven, Netherlands, or any other suitable white
light source having a similar spectral range. FIG. 1A schematically
illustrates the spectral output of the high-pressure mercury
UHP.TM. 100 Watt lamp. It will be appreciated that all other types
of high-pressure mercury lamps, such as the VIP lamp available from
Osram Berlin, Germany, have similar spectra and similar designs, so
the following examples apply to all such lamps.
[0028] The examples herein are described in the context of
high-pressure mercury type lamps because such lamps are most
commonly used in projection display devices. However, some aspects
of the embodiments described herein, e.g., the use of significantly
overlapping primary color spectral ranges, may be applied in
designing color filtering arrangements for other devices using
other types of light sources. For example, aspects of the invention
may be applied to devices using Xenon (Xe) type light sources, as
are known in the art, having a spectral output as illustrated
schematically in FIG. 1B: It will be appreciated by persons skilled
in the art that the output spectra of the Xe type lamp of FIG. 1B
is much smoother, and thus less difficult to accommodate, for the
purpose of designing partially-overlapping spectra: in accordance
with embodiments of the invention, than the relatively "peaky"
output spectra of the mercury type lamp of FIG. 1A.
[0029] For simplicity, the following description ignores possible
non-uniformities in the spectral transmission properties of the
optical elements used by the device of the invention. It will be
appreciated, however, that such non-uniformities are not
significant.
[0030] By appropriately selecting a desired set of partially
overlapping primary colors, and by appropriately designing a color
filtering arrangement to produce such primary colors, the method
and device of the following exemplary embodiments of the invention
may be implemented in conjunction with any color display system
known in the art. In some embodiments of the invention, the display
system may use more than three, partially overlapping primary
colors. Display systems using more than three primary colors are
described in International Application PCT/IL01/00527, entitled
"Device, System and Method For Electronic True Color Display",
filed Jun. 7, 2001, published Dec. 13, 2001 as WO 01/95544, and in
International Application PCT/IL01/01179, entitled "Spectrally
Matched Print Proofer", filed Dec. 18, 2001, published Jun. 27,
2002 as WO 02/50763, assigned to the assignee of the present
application, the entire disclosure of both of which is incorporated
herein by reference.
EXAMPLE 1
Six Primaries, Six-Panel Wide Gamut Display
[0031] The following example illustrates selection of primary color
wavelength ranges for a wide gamut display using six Spatial Light
Modulator (SLM) panels, wherein each panel produces one primary
color. This configuration may allow full coverage of the typical
color gamut of a projection film e.g., a motion picture positive
film, enabling a projection display to produce virtually all the
colors that can be produced by projection film, as described below.
FIG. 2 schematically illustrates an optical configuration of a
device in accordance with this embodiment of the invention. The
exemplary configuration of FIG. 2 is particularly adapted for
devices using reflective-LCD type SLM panels.
[0032] According to embodiments of the invention, light from an
illumination unit 201, which may include any suitable white light
source known in the art, as described above, may be imaged onto LCD
panels 206, 207, 208, 209, 210 and 211, via a relay lens 202, a
reflection-transmission element, e.g., a polarizing beam splitter
(PBS) 203, and a color separation arrangement e.g., "X"
color-separator cubes 204 and 205. Each of LCD panels 206, 207,
208, 209, 210 and 211 may include an array of pixels, as is known
in the art, which may be selectively activated to produce a
reflective pattern corresponding to one of a plurality of primary
color images. In the example described herein, each LCD panel may
be separately activated by a control unit (not shown in the
drawings) to produce a reflective pattern corresponding to one of
six independent primary color images, in accordance with an input
signal representing a six-primary-color image. Such an input signal
may be generated using any of the methods described in the
above-referenced International Patent Applications, e.g., by
converting a three-primary-color image signal into a
six-primary-color image signal. As described below, each reflective
pattern may modulate a corresponding primary color light beam to
produce a corresponding primary color image component.
[0033] PBS 203 may split the white light from unit 201 into a
reflected "s"-polarized component and a transmitted "p"-polarized
component, as is known in the art. The "s"-polarized component may
be separated by "X" color separation cube 204 into light beams of
three different wavelength ranges, which correspond to three of the
six primaries used in this embodiment of the invention. The
operation of "X"-cubes as multiple filtering elements for color
separation is well known in the art and commercially available. An
example of such commercially available component is the Optec.TM.
Standard Cubic Dichroic (X-Cube) Beam-splitter available from
Richter Enterprises, Texas, United States.
[0034] It may be appreciated by those skilled in the art that any
other suitable color filtering a arrangement may be used, for
example, to implement a desired number of primary colors. For
example, the color filtering arrangement may include one "X" color
separation cube and a dichroic mirror, as are known in the art, to
separate the polarized components into five primary color light
beams.
[0035] Each pixel of LCD panels 206, 207 and 208, when activated to
an "on" state, may convert the "s"-polarized light into
corresponding "p"-polarized light, as is known in the art and may
reflect the converted light back via "X" color separation cube 204.
The three primary color light beams exiting "X"-cube 204, which
beams are modulated in accordance with three, respective, primary
color image components, may be transmitted through PBS 203 towards
projection lens 212; Analogously, the transmitted "p"-polarized
light may. be separated by "X" color separation cube 205 into three
different color light beams, corresponding to the remaining three
primary colors. Each pixel of LCD panels 209, 210 and 211, when
activated to an "on" state, may convert the "p"-polarized light
into corresponding "s"-polarized light, as is known in the art and
may reflect the converted light back via "X" color separation cube
205. The three color light beams exiting "X"-cube 205, which beams
are modulated in accordance with three, respective, primary color
image components, may be deflected by PBS 203 towards projection
lens 212. The projection lens may project all six modulated colored
light beams, i.e., all six primary color image components, onto a
viewing screen (not shown in the drawings).
[0036] It should be noted that the separate wavelength ranges
produced by "X"-cube devices are inherently non-overlapping.
Therefore, in the example described herein, there is no spectral
overlap among the three primary color spectra produced by each
"X"-cube, 204 or 205. Therefore, in this configuration, the desired
partial overlap between primary color spectra, in accordance with
embodiments of the invention, may be achieved by overlaps between
the primary color spectra produced by "X"-cube 204 and the primary
color spectra produced by "X"-cube 205. It will be appreciated by
persons skilled in the art that essentially any desired overlapping
can be achieved between primary color spectra produced by two
"X"-cubes.
[0037] FIGS. 3A and 3B schematically illustrate primary color
wavelength spectra for a six-primary color display using the
configuration of FIG. 2. FIG. 3A shows the wavelength spectra of a
set of three non-overlapping primary colors having spectral ranges
of approximately 400-500 nm, approximately 500-550 nm, and
approximately 575-750 nm, respectively, which may be produced by
one color separation cube e.g., "X"-cube 204 in FIG. 2. FIG. 3B
shows the wavelength spectra of an additional set of three
non-overlapping primary colors having spectral, ranges of
approximately 450-520 nm, approximately 520-620 nm and
approximately 620-750 mm, respectively, which may be produced by
another color separation cube, e.g.,"X"-cube 205 in FIG. 2. As
shown in the drawings, there is significant overlap between the
spectra of each of the primary colors in FIG. 3A and at least one
of the primary colors in FIG. 3B, and vice versa. For example, the
spectrum at the bottom of FIG. 3B partially overlaps, at different
ranges, the two bottom spectra in FIG. 3A. It will be appreciated
by persons skilled in the art that, despite the significant
overlaps between primaries, the six spectral ranges illustrated in
FIGS. 3A and 3B represent six distinct primary colors. According to
embodiments of the invention, the specific color choices and
partial overlap design of the primary color wavelength ranges shown
in FIGS. 3A and 3B may result in a significantly wider color gamut
and image brightness, compared to prior art color display devices,
as described below.
[0038] FIG. 4 schematically illustrates the resulting color gamut
of the primary color spectra of FIGS. 3A and 3B. As clearly shown
in FIG. 4, the color gamut produced by a typical positive motion
picture film is completely covered by the gamut of the six primary
colors of FIGS. 3A and 3B. As further shown in FIG. 4, the white
point coordinates obtained by the sum of all primaries are x=0.313
and y=0.329. The luminance values for the colors obtained by this
configuration are in general equal to or higher than the luminance
values that can be obtained for the same colors from a typical
projection film, e.g. a positive motion picture film. Thus, in
general, all the colors that can be reproduced by projection film
can be reproduced by devices using the primary color selections of
FIGS. 3A and 3B, both in terms of color coordinates and in terms of
intensity. It should be appreciated that although the primary color
selections of FIGS. 3A and 3B provide desirable results in terms of
image color and brightness, there may be other suitable selections
of six primary colors, wit partial overlap, that provide similar
(or even better) results, in accordance with specific
implementations.
EXAMPLE 2
Multiple Primaries, Single Panel, Sequential Display
[0039] The following example illustrates implementation of the
present invention in the context of a six-primary-color sequential
display. In a sequential display system, the colors are typically
produced by a sequential color switching mechanism, e.g. a color
wheel or a color drum, which transmits each color for a preset time
period (window) within each field of the video stream. In such a
system, the relative intensities of the primary colors may be
adjusted by adjusting the relative sizes of a plurality of color
filter segments on the color wheel. The single panel configuration
may be implemented with either LCoS (Liquid Crystal on Silicon) or
micro-mirror (CDM.TM.) type panels, which are available, for
example, from Texas Instruments, U.S.A., as is known in the art. In
this example, the spectra of FIG. 3A and 3B are produced by six
filter segments, wherein each filter segments transmit one of the
spectra of FIGS. 3A or 3B. The operation of multi-primary
sequential projection color displays is discussed in detail in the
above-referenced International Applications.
[0040] For a multiple-primary system, there may be numerous
combinations of color filters, having varying relative segment
sizes, to produce a desired viewed color, e.g., a desired white
color temperature. The relative segment sizes of the color filters
may affect the over-all brightness of the display, e.g., relative
to the utilized portion of the light generated by the light source.
The relative segment sizes of the color filters may also affect the
relative intensity of each of the primary colors. Thus, the
relative segment sizes of the color filters may be selected to
provide a desired, e.g., maximal, over-all brightness of the,
display and/or a desired relative intensity of each of the primary
colors, for example, to optimize specific implementations, as
described below.
[0041] In order to calculate the reproducible color gamut the light
source spectrum, e.g. as shown in FIG. 1A or FIG. 1B, may be
multiplied by a transmission spectrum (not shown) of the optical
engine used, e.g., the single panel DMD.TM. type optical engine.
Such multiplication may exclude the influence of the color
generating elements, e.g., the color filters. The resulting
spectrum may then be multiplied by the transmission spectra of the
color filters to provide a set of primary reproducible spectra
corresponding to the primary colors, respectively. As is known in
the art, CIE 1931 x and y values of the color points corresponding
to the primary reproducible spectra may be calculated to determine
the reproducible color gamut. The relative segment sizes of the
color filters may be selected according to the primary reproducible
spectra, so as to provide a maximal over-all brightness, e.g., when
all the primary colors are at their maximum levels, and to provide
a desired relative intensity for each primary color.
EXAMPLE3
Five Primaries, Single Panel, Sequential Display
[0042] It should be noted that the use of six primary colors is
advantageous because six primaries may provide more flexibility in
color adjustment compared to systems using less than six primaries.
However, according to some embodiments of the invention, there are
certain advantages in using less than six primary colors. One such
advantage is that more time can be allocated to each primary in a
sequential projection system, thereby improving the temporal
resolution (bit depth) of the displayed image. According to this
embodiment of the invention, five primary colors may be used. For
example, the five primaries may include a blue color having a
wavelength spectral range from about 400 nm to between 460 nm and
540 nm, a cyan color having a spectral range from between 400 nm
and 460 nm to between 500 nm and 560 nm, a green color having a
spectral range from between 480 nm and 520 nm to between 540 nm and
580 nm, a yellow color having a spectral range from between 500 nm
and 550 nm to 650 nm or more, and a red color having a spectral
range from between 580 nm and 620 nm to 700 nm or more.
[0043] FIG. 5 schematically illustrates transmission spectra for
five filter segments that may be used by a five-primary-color
display in accordance with embodiments of the invention. The filter
selections of FIG. 5 may enable reproduction of a color gamut that
is slightly wider than the standard NTSC color gamut, especially in
the yellow-red regions, e.g., the yellow-red colors that can be
displayed by this system may be more saturated than those allowed
by the standard NTSC gamut as shown schematically in FIG. 6. In
order to balance the white point with all primaries filly
transmitted, as described above, the relative segment sizes of the
blue, cyan, green, yellow and red primaries in this example are
0.8, 0.8, 0.6, 1.1 and 1.7, respectively. This configuration may
allow a brightness gain of about 40 percent over the six-primary
color wheel configuration described above with reference to the
primary color selections of FIGS. 3A and 3B. Furthermore, the
brightness of a display device using the five primary color filter
selections of FIG. 5 may produce image brightness about 1.9 times
higher an the image brightness of a three-primaries (e.g., RGB)
projection display using NTSC primary colors (with relative sizes
of 0.5, 1, and 1.6 for the blue, green and red color filter
segments, respectively). According to these embodiments, the
increase in brightness may be achieved by increasing the amount of
overlap between the transmission spectra of the different color
filter segments, resulting in a slightly narrower color gamut than
the six-primary color gamut shown in FIG. 4
[0044] Another possible application of multiple primaries is for
significantly increasing he brightness of a device producing the
color gamut of a conventional REC-709 or similar display. FIG. 7
schematically illustrates filter transmission curves according to
this embodiment of the invention. The filter segments in this
example are used with relative segment sizes of 1, 0.9, 0.4, 1 and
1.7 for the blue, cyan, green, yellow and red primary color filter
segments, respectively. The resulting color gamut of this
embodiment is illustrated schematically in FIG. 8. It will be
appreciated that the color gamut produced in this example is still
larger than the REC-709 color gamut, particularly in the yellow and
cyan regions. However, the brightness that may be achieved by this
display is about 40 percent higher than the brightness of a
corresponding display using only the standard REC-709 RGB filters
(with relative segment sizes of 0.8, 0.7, 1.5 for the blue, green
and red primary color filter segments, respectively).
EXAMPLE 4
Four Primaries, Single Panel, Sequential Display
[0045] In some embodiments of the invention, a four primaries
display may also provide many advantages for the multi-primary
color display. According to these embodiments, improved brightness
may be achieved by the addition of a yellow primary color filter
segment to the RGB segments. White balance may be achieved by
adjusting the relative segment sizes, as described above. For
example, the four primary colors may include a 540 nm, a green
color having a spectral range from between 480 nm and 520 nm to
between 540 nm and 580 nm, a yellow color having a spectral range
from between 500 nm and 550 nm to 650 nm or more, and a red color
having a spectral range from between 580 nm and 620 nm to 700 nm or
more.
[0046] FIG. 9 schematically illustrates transmission curves of four
primary color filter segments that may enable the device to produce
a gamut comparable to the NTSC standard gamut, as schematically
illustrated in FIG. 10, which is similar to the five-primary color
gamut shown in FIG. 6. White balance may be achieved, as described
above, by using relative segment sizes of 1.2, 0.8, 1 and 1 for the
blue, green, yellow and red primary color filter segments,
respectively. This configuration may result in an image brightness
gain of about 90% over the brightness level of a
white-balance-corrected NTSC RGB color gamut (with relative segment
sizes of 0.6, 1 and 1.5 for the blue, green and red primaries,
respectively), i.e., the brightness gain in this example is similar
to the brightness gain of the five-primary color display described
above.
[0047] In other embodiments of the invention, a four-primary color
display may be used to increase the brightness of an REC-709 gamut
by adding a yellow primary color filter segment. The filters
transmission curves for this alternate embodiment are schematically
illustrated in FIG. 11. The spectral ranges of FIG. 11 may be wider
than the spectral ranges of FIG. 9 in order to reproduce a wider
color gamut. The relative sizes of the color filter segments used
in this example are 1.5, 0.7, 1.2 and 0.9 for the blue, green,
yellow and red primary color filter segments, respectively. The
resulting color gamut of this example is schematically illustrated
in FIG. 12. It will be appreciated that this gamut is still larger
than the REC-709 color gamut, particularly in the yellow regions,
as shown in FIG. 12. The brightness that may be achieved by this
display is about 50 percent higher than the brightness of a display
using only the REC-709 RGB color filter segments (with relative
segment sizes of 0.8, 0.7, 1.5, for the blue, green and red primary
color segments, respectively).
[0048] While certain features of the invention have been
illustrated and described herein, many modifications,
substitutions, changes, and equivalents will now occur to those of
ordinary skill in the art. It is, therefore, to be understood that
the appended claims are intended to cover all such modifications
and changes as fall within the true spirit of the invention.
* * * * *